All the known eddy current machine load control devices can only control the exciting current of an electrical machine. The braking moment of the machine lags behind the exciting current in time due to a considerable time constant of the eddy current circuit. As a result, the conventional devices, based on the eddy current control, are unable to effect a rapid change of the braking moment.
There is known an eddy current machine load control device (cf. USSR Inventor's Certificate No. 514,399, Cl. HO2K 49/02) comprising a comparator having a first input for the supply of voltage of a predetermined magnitude and an output electrically coupled via an automatic voltage regulator to a controlled input of a controlled power source of the electrical machine. An output of an electrical machine load transducer is connected to a second input of the comparator. The automatic voltage regulator is a proportional controller responding to the difference between the predetermined voltage and a feedback voltage at the output of the load transducer. The latter is a discrete transducer intended to convert the magnetic flux to an electric signal, and operates only at maximum or minimum magnitudes of the magnetic flux, which are proportional to minimum or maximum loads.
As a result, the device under review can only set a minimum or maximum load, being unable to automatically maintain the load at a prescribed level. Besides, a change in the operating conditions of the electrical machine necessitates modifications in the load transducer, which complicates the process of control.